Dusting devices

Suitable environmental conditions should be maintained by installation of effective air-extraction systems, with discharge points sited to avoid contamination of other products and processes. Ritration or other systems should be installed to retain dust The plant should be properly serviced and maintained. Care should be taken to contain any dust loosened when filters are removed or replaced and to avoid dust falling back on to product from extraction duct-work. The use of tablet and capsule de-dusting devices is recommended. 

A de-dusting device for removing fines from pellets and granules... 

Fig. 3. Enhancement of the performance of an elutriator using POSTEC s de-dusting device.

Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. The element has been used in devices for eliminating static charges in textile mills, etc. however, beta sources are both more commonly used and less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, minimizing hazards to the user. 

Other Centrifugal Collectors. Cyclones and modified centrifugal collectors are often used to remove entrained Hquids from a gas stream. Cyclones for this purpose have been described (167—169). The rotary stream dust separator (170,171), a newer dry centrifugal collector with improved collection efficiency on particles down to 1—2 pm, is considered more expensive and hence has been found less attractive than cyclones unless improved collection in the 2—10-pm particle range is a necessity. A number of inertial centrifugal force devices as well as some others termed dynamic collectors have been described in the Hterature (170). 

Scmbbers make use of a combination of the particulate coUection mechanisms Hsted in Table 5. It is difficult to classify scmbbers predominantly by any one mechanism but for some systems, inertial impaction and direct interception predominate. Semrau (153,262,268) proposed a contacting power principle for correlation of dust-scmbber efficiency the efficiency of coUection is proportional to power expended and more energy is required to capture finer particles. This principle is appHcable only when inertial impaction and direct interception are the mechanisms employed. Eurthermore, the correlation is not general because different parameters are obtained for differing emissions coUected by different devices. However, in many wet scmbber situations for constant particle-size distribution, Semrau s power law principle, roughly appHes ... 

AH operations producing dust require the usual measures to prevent dust in the atmosphere exceeding the allowable daily concentration. If this is not feasible, personal protection devices should be used. Especially when hydroquinone is present as a powder, adequate eye protection should be provided. 

The limitation to disk constmctions with a laser beam reflected at the disk surface is a large drawback, however. This prevents the insensitivity against dust and dirt, which is well known from current optical storage devices with a laser beam reflected after penetration of the transparent substrate. 

Environmental Protection. Fumes resulting from exposure of anhydrous aluminum chloride to moisture are corrosive and acidic. Collection systems should be provided to conduct aluminum chloride dusts or gases to a scmbbing device. The choice of equipment, usually one of economics, ranges from simple packed-tower scmbbers to sophisticated high energy devices such as those of a Venturi design (11). 

Inhalation of extremely fine carbide, cobalt, and nickel powders should be avoided. Efficient exhaust devices, dust filters, and protective masks are essential when handling these powders. 

Cement plants in the United States are now carehiUy monitored for compliance with Environmental Protection Agency (EPA) standards for emissions of particulates, SO, NO, and hydrocarbons. AH plants incorporate particulate collection devices such as baghouses and electrostatic precipitators (see Air POLLUTION CONTROL methods). The particulates removed from stack emissions are called cement kiln dust (CKD). It has been shown that CKD is characterized by low concentrations of metals which leach from the CKD at levels far below regulatory limits (63,64). Environmental issues continue to be of concern as the use of waste fuel in cement kilns becomes more widespread. 

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